Q: What causes the Aleutian low to form? During
the Northern Hemisphere's winter, why does it become stronger compared to its
strength in summer?

A: The "semiperminent" Aleutian Low, which sits
nearly all winter south of Alaska's Aleutian Island chain, forms and grows when
the temperature contrast between land and sea is greatest. Air over the North
Pacific, much warmer than North America or Asia in winter, rises to form low
pressure there. In summer, as the land warms up, the land-sea temperature contrast
is less, and the Aleutian Low weakens. It is replaced by the Pacific High, which
forms farther south between Hawaii and the USA due to similar but reverse processes
 the sea there is relatively cooler than North America in summer in air
sinks over the cool water, forming high pressure.

To understand more about high and low pressure systems,
visit USATODAY's Storms
and fronts index, which has links to a number of graphics explaining how
they form and their differences.

Q: What type of baroclinic low is reflected at the surface
as a low and supported by an upper-level closed -circulation high?

A: The type of low
pressure system you are describing is known as a thermal low. These weak
lows form in very hot, sunny weather. They are most common in the Desert Southwest.
As you rise in altitude above the thermal low, the curvature of the height isopleths
slowly changes from cyclonic to anticyclonic. The reason for this is that unlike
most lows, thermal lows are warm core systems, which cause the lows to weaken
with height and eventually become anticyclonic. The upper-level highs formed
by the anticyclonic curvature of the height isopleths do not spawn or support
thermal lows. Thermal lows are supported most by hot temperatures and heating
by the sun.

(Answered by Chad Palmer, USATODAY.com Weather Team,
8-10-99)

Q: What causes anti-cyclogenesis? I guess the question
that I would like answered is, what causes the vertical stacking of the low
pressure with height, which causes its decay, in comparison to the tilting of
the trough axis (into the cold air) which causes its intensification?

A: Quite simply, the vertical stacking of low
pressure with height is a normal part of a storm's life cycle. How quickly
the storm stacks and begins to decay depends of the vertical wind structure,
the location and orientation of the warm air to the east of the storm (also,
how quick the warm air gets cut off) and the topography where the surface storm
is moving. Smooth, flat terrains, such as water or flat land, produce less friction
and are more favorable for storms while mountains tend to weaken storms.

The typical life cycle of an area of low pressure is as
follows.

An upper-level cold air injection helps form an upper-level
trough and vorticity along with warm advection in the lower levels downstream.

The vorticity (or in some cases, an upper-level low)
combines with the warm low-level advection downstream to form an area of low
pressure at the surface that is vertically tilted toward the upper-level low
farther back into the cold air.

Friction slows the surface storm down, allowing the
upper-level low to catch up with it and become vertically stacked.

Once the storm becomes vertically stacked, the surface
storm often redevelops farther back into the cold air, thus cutting off the
needed low-level warm advection. This is known as an occlusion. Since the
vorticity is directly above the storm, the needed vorticity advection is downstream
of the storm. These two factors cause the storm to spin down an lose its intensity.

There are many other factors which affect the intensity
and life cycle of the storm too numerous to mention here. For further research
and the mathematical equations that predict storm intensities, any atmospheric
dynamics book is a good place to start. A popular textbook that is used to teach
meteorology at many colleges is An Introduction to Dynamic Meteorology by
James R. Holton.

(Answered by Chad Palmer, USA TODAY Weather team, Nov.
21, 1998)

Q: What do the terms isentropic and orthogonal mean
relating to weather/weather forecasting? Thanks!

A: Isentropic lift is kind of complicated because it refers
to potential temperature or lines of equal potential temperature. Potential
temperature refers to a parcel of air that is brought down to a pressure of
1000 mb and warms adiabatically as it descends. This coordinate system is used
when the atmosphere is stable. If a large
current of air is flowing from a region of low potential temperature to a region
of higher potential temperature, then rising motion is occurring which is known
as isentropic lift. You hear this term often in weather discussions. If there
is prolonged or very strong isentropic lift, then rain or snow is a pretty good
bet.

Orthogonal flow is much simpler as it means flow that is
perpendicular to the point of reference. For example, westerly winds blowing
into a north-south line of mountains would be orthogonal flow into the mountains.
Orthogonal flow often means rain or snow if mountains
or fronts are involved, but not always. Orthogonal
flow usually produces rising motion on one side of the mountains and sinking
motion on the other. Downslope and upslope
graphics illustrate the effects of orthogonal flow into mountains.

(Answered by Chad Palmer, USA TODAY Weather team)
(11-21-98)

Q: I would like to know more about so-called "hybrid
storms." These storms occur during the winter over the Atlantic and Pacific
Ocean and the Mediterranean Sea and act like hurricanes, but there's no name
assigned to them. What's the difference between a hybrid storm and a real hurricane?
By the way wasn't the infamous Halloween storm the remnants of Hurricane Grace?
Was the hybrid or "Christmas" storm of Dec. 23-24, 1994 a hurricane?

A: Hybrid storms are neither tropical nor extratropical
cyclones, but the offspring of both. They come in all sizes and intensities
and most form in late fall or winter. Feeding off the energy from atmospheric
temperature contrasts and latent heat, hybrid storms can rapidly intensify into
"winter hurricanes" with heavy snow and strong winds. Many of the large East
Coast nor'easters and "bomb
cyclones" are examples of hybrid storms. A USA TODAY online
story has much more about these strange storms that defy easy classification.

(Answered by Chris Cappella, USA TODAY Information Network,
4-6-97)

Q: I am working on a project but I have had trouble
finding the answer to this question: Does centripetal force (that causes objects
to follow a circular path around a central point, such as a rock spinning in
a sling) have anything to do with Hurricanes? If not, why don't the storm clouds
just fly off in all directions?

A: Centripetal force is an important part of any cyclone
-- a system of winds around a low pressure area -- including hurricanes. You
are correct, if nothing were pushing the air inward toward the center of the
storm, the air would try to go in a straight line, just as a car on an icy road
slides of the road when a driver tries to go around a curve too fast. In storms,
the centripetal acceleration that keeps the winds going in a circle around the
low pressure comes from the pressure gradient
force. A hurricane, like any storm, has an area of low pressure in the center
surrounded by pressures that grow higher and higher as you go outward from the
center. Differences in pressures create forces that push air from high to low
pressure; that's what causes the winds. The chapter on "The Atmosphere in Motion"
in Meteorology Today by C. Donald Ahrens has a good discussion of all
of the forces acting on winds. The book is the most popular beginning college
meteorology text in the U.S. Our hurricane
index has links to more details on how these storms work. (4-6-97)

Q: Can you explain to me what a northeaster is? why
it's called that? how they are formed? and what conditions are needed to form
them?

A: Northeasters are storms along the U.S. Atlantic Coast
from the Carolinas northward. The name refers to the northeast winds off the
Atlantic Ocean that normally bring the storms' worst weather. Like all Northern
Hemisphere storms, the winds are going counterclockwise around the low-pressure
center. This means that when the center is south of your location along or near
the coast, the winds come from the east or northeast. As the center moves northward,
the winds shift around to blow from the north, the northwest and the west. While
the northeast winds bring in humid ocean air, which feeds precipitation; the
northwest winds tend to bring cold, dry air that clears the sky. A USA TODAY
online graphichas more details
on these storms. Along Florida's Atlantic Coast, the term "northeaster" often
refers to strong winds blowing from the northeast caused by the clockwise flow
around a strong high-pressure area over the East Coast from the Carolinas northward.
These winds often bring rain and high surf. (4-1-97)

Q: If I understand correctly, a high pressure area is
caused by sinking, heavier cool air relative to the air around it. Why is it
then that we in central Virginia are enjoying unseasonably warm temperatures
in the mid 70's while in a High?

A: You are correct, a high pressure area at the surface
is created as air sinks from above. But, as the air sinks, it warms. This warming
of the air helps some in warming the ground. Even more important, the warmed
air keeps clouds from forming or even evaporates clouds. This is why the sky
is generally sunny in high-pressure areas. (Haze and fog can form, however.)
The clear skies allow plenty of solar energy to reach the ground, warming it.
High pressure areas can be either cold or warm. The highest surface pressures
are recorded in the polar regions when very heavy, dense air piles up. The warming
caused by the air's sinking takes only a little of the edge off the bitter cold.
A USA TODAY online graphic shows what's going on in areas of high
and low pressure. Our storms and fronts index
has links to information on the relation between air pressure and weather.
(3-28-97)

Q: Can you tell me if the high and low pressure systems
are more intense in winter or in summer? Right now I'm looking at some weather
maps and I see highs with 1030 mb. Thanks.

A: Low pressure
systems are much more intense during winter. The reason for this is the temperature
contrast between the equator and the poles is the greatest during winter since
the polar regions are in total darkness. This allows massive Arctic airmasses
to form and slide south toward the equator. Once Arctic
air slides south, it often clashes with warm, moist air from the tropics
and gives birth to sometimes very intense storms.

Arctic high pressure systems are the strongest during winter
due to the total darkness mentioned above. The Bermuda
high,however, is weak during winter, but often becomes very strong during
summer. The Bermuda high is the main culprit behind the hot, humid summers typical
of the eastern USA. Our storms and fronts homepage
has more on how high and low pressure systems work.

(Answered by Chad Palmer, USA TODAY Weather team)
(3-15-97)

Q: What is the difference between a low pressure center
and a trough of low pressure? What accounts for these differences? Are they
similar to ocean waves and swells?

A: By definition, a low
pressure center is an area where the barometric
pressure is higher on all four sides as you move away from the center. A
trough of low pressure has higher
barometric pressure on three of the four sides, but lower pressure on one side.
Troughs of low pressure often extend generally southward from a center of low
pressure in the Northern Hemisphere..

A center of low pressure forms when conditions are very
favorable for storm development or intensification. If conditions are less favorable,
a trough of low pressure may form instead of a center of low pressure.

The ocean and the atmosphere are similar in that they both
behave as "fluids". Waves generated in the atmosphere move along just as they
do in the ocean. However, the ocean is much more dense than air, which creates
many differences. The ocean is also heated from the top, which creates a very
stable environment in the ocean water below the ocean's surface. The atmosphere,
on the other hand, is heated from below by the sun, which creates much more
turbulence and vertical motion. Waves in the ocean are primarily generated by
winds blowing across the ocean's surface, but earthquakes and volcanoes on the
ocean floor can also generate very large waves. Our storms
and fronts homepage has more on storms in the atmosphere while our ocean
weather home page has more on ocean waves and conditions.

(Answered by Chad Palmer, USA TODAY Weather team)
(3-5-97)

Q: We are students studying weather in Centerville,
Md. We would like to know how temperature and pressure are related?

A: Air temperature and pressure aren't related in any simple
way. Low pressure is at the heart of any storm. But in tropical storms this
area of low pressure is warmer than surrounding areas. In storms outside of
the tropics, the air around the low pressure is cooler than areas around it.
Very cold air that forms over the far north creates high pressure. But, high
pressure areas can also be hot. Our storm systems
and fronts page has links to a lot more information on air pressure and
different kinds of weather. (2-23-97)

Q: Jack, is a cold front usually associated with a low
pressure system and a warm front with a high pressure or is it just the opposite.
Please explain why. Thanks.

A: Both cold
fronts and warm fronts are
usually associated with areas of low
pressure. The main reason for this classification system is that surface
troughs form along fronts. The
circulation between areas of high pressure
and low pressure determines the prevailing wind and depending on their positions,
they can usher in very warm air behind a warm front and very cold air behind
a cold front. Our storm systems and fronts homepage
has more information about different kinds of weather systems and fronts.

(Answered by Chad Palmer, USA TODAY Weather team)
(2-19-97)

Q: Since heat rises and cold air settles, why are mountain
tops cold while valleys are hot? Thanks.

A: You are correct, air that is warmer than its surroundings
tends to rise while colder air sinks. However, that general rule assumes equal
atmospheric pressure. Gravity acting on the air molecules in our atmosphere
causes air pressure. Barometric pressure
decreases the higher above the surface you go because there are fewer air molecules
pressing down. Air density also decreases
with altitude. If you go to the humidity calculations
page and scroll down to formula (13), you can see the mathematical relationship
between pressure and air density. Since air density (you can think of this as
being how heavy the air is) decreases with lower pressure, the air on mountain
tops is not more dense (or heavier) than the air below. Even though it's colder,
it does not sink. Click here for a file
with more information on air temperature.

Q: I know a lot about the weather. Though there is one
thing I don't quite understand. How come in the summer, the wind hardly ever
blows, but when it becomes cold outside, the wind blows almost constantly?

A: The main reason for lack of wind in the summer and often
windy conditions in the winter is the change in the main storm track across
the USA during the different seasons. The jet
stream retreats to the north during summer and as a result, most areas of
low pressure also move across
the northern USA and Canada. In winter, the jet stream often dives south and
brings the storm track as far south as the Gulf of Mexico. The difference
in pressure between areas of low pressure and high
pressure is what generates wind. During summer, when the jet stream and
storm track is far to the north, a large area of high pressure, known as the
Bermuda High, dominates the weather picture
over Alabama. Pressure differences are very small across this large area of
high pressure. As a result, wind speeds are very light. In winter, when the
jet stream and storm track is often near Alabama, large pressure differences
caused by areas of low pressure often breed very strong, gusty winds. Our storm
systems and fronts homepage has more on storms and our wind
and jet stream homepage has more on wind.

(Answered by Chad Palmer USA TODAY Weather team)
(1-9-97)

Q: What is the difference between an Alberta Clipper
and the Arctic Express I hear about every winter?

Q: Dear Jack, I was wandering what an Alberta Clipper
is?

A: An Alberta
Clipper is a fast-moving area of low
pressure that develops in Alberta, Canada during winter. The Arctic Express
refers to the flow of Arctic air
from the far north south over the USA in winter. These frigid airmasses
often bring record breaking cold temperatures to many locations in the USA.
Sometimes, Alberta Clippers can enhance an Arctic outbreak over the USA as they
scoot across the country.

(Answered by Chad Palmer, USA TODAY Weather team)
(1-4-97)

Q: Is there any scientific evidence to support the theory
that weather fronts push viruses and bacterial infections across the nation.
It seems that when a weather front passes over, there is an increase of illnesses,
especially flu, sinusitis and lower respiratory infections.

A: This is an interesting question that I just don't know
the answer to. So far I haven't found an answer, but still have places to look.
I've received some other questions about weather and health and am trying to
find a good source of reliable information for answers to these questions. When
I do, we'll set up a weather and health index. (1-1-97)

Q: Hurricanes rotate counter-clockwise in the Northern
Hemisphere and clockwise in the Southern Hemisphere. This effect was named after
the scientist who "discovered" this phenomenon. Who was he and why do hurricanes
rotate in opposite directions North and South of the equator? Thanks for your
help.

A: Gustave-Gaspard Coriolis, a French scientist, didn't
actually discover the directions storm winds blow north and south of the equator,
but in 1835 he became the first to describe mathematically what's going on,
giving his name to the Coriolis effect. Sometimes it's called the Coriolis force.
A USA TODAY online graphic explains more about the Coriolis
effect. With it you will find a link to a "bad meteorology" web age by Alistair
Fraser of Pennsylvania State University that explains why the Coriolis effect
does not make water flow down a sink's drain or a toilet in different directions
on opposite sides of the equator, as many believe it does. It affects on large
systems such as hurricanes. (12-28-96)

Q: As a teacher of Earth Science I recently came upon
a question, posed by one of my students, which I have had difficulty answering.
In fact, I have put feelers out on the web and all the responses to date have
told me to ask someone else and have made suggestions as to where to go for
help. That is how I have come to you. The question is- does an object, such
as a parcel of air, which is traveling due east or due west, get deflected to
its right in the northern hemisphere as though the Coriolis effect we re acting
upon it? If so, why? There appears to be no difference in the rotational speeds
if the object is not moving north or south, yet somewhere I believe I have come
upon a reference to the fact that it would be deflected. Unfortunately, I cannot
recall the reference. Can you help? Thanks

A: The Coriolis effect is one of the hardest-to-understand
meteorological concepts. For anyone who wants to know what it is, click
here for a graphic and text with basic details. This graphic doesn't quite
answer your question, but the technique used is the way to demonstrate that
yes, the Coriolis effect does deflect an object moving directly east or west,
unless it's moving along the equator.

The best explanation I found is in a textbook that's no
longer in print, Understanding Our Atmospheric Environment, Second Edition,
by Morris Neiburger, James Edinger, and William Bonner. It was published by
W.H. Freeman and company in 1982. You might be able to find a copy in a good
library or obtain one via interlibrary loan.

On page 188, the book describes the Coriolis effect by
showing how a projectile, such as a rocket, would appear to move over the Earth's
surface. The authors write: "If the projectile is aimed parallel to a parallel
of latitude (other than the equator) the deflection will also be to the right
in the Northern Hemisphere and to the left in the Southern Hemisphere. It is
hard to draw a diagram showing this on a sphere. However, the same effect occurs
on a rotating disc." The book has a drawing showing such paths drawn on a disc
that has been rotated.

You could set up a similar experiment with your students
using a round piece of cardboard, a ruler to make sure straight lines are drawn,
and a felt-tip pin to draw lines on the rotating, cardboard disc. You could
use a record player - remember the devices that we used to use to play records
before CDs came along? But, the rotation would be too fast to really see what
happens. A better set up would be to have one student rotate the disc by hand,
at as steady a rate as possible, while another uses the ruler and pen to draw
straight lines in various directions, as shown in our graphic.
Experimenting with different rotation rates and speeds of line drawing should
be interesting. Let me know how this works. (11-13-96)

Q: The remnants of Hurricane Lili recently caused heavy
damage in parts of northern Europe. Can a hurricane survive the North Atlantic
or are they just strong low pressure systems by the time they hit the United
Kingdom? Do low pressure systems ever "make the circuit?" That is continue around
northern Europe and Siberia to affect us again in the Pacific Northwest?

A: Hurricane Lili weakened
to a tropical storm and then became an extratropical storm north of the Azores
before hitting Ireland, Great Britain and then northern Europe last month. I
don't know of any cases in which a storm has still been a hurricane when it's
hit the British Isles and Europe. But, in some cases, including Lili, the winds
have been hurricane force or gusting to hurricane force, or 74 mph or higher.
Tropical storms need warm water to remain tropical. A USA TODAY online graphic
explains the differences between tropical and
extratropical storms.

I don't know of any documented cases of surface storms
going around the Earth. But, there have been cases of western Pacific typhoons
moving to the west, then northward, becoming extratropical storms and then coming
back to hit the U.S. Pacific Northwest. For more on one such storm, click
here to go to our page on Pacific Coast storms. Then scroll down to the
headline reading "Hurricane force winds that hit the Pacific Coast."

Upper air disturbances,
however, do circle the globe. The March 12 -14, 1993 "storm
of the century" in the eastern USA was triggered when two potential vorticity
anomalies (upper-air disturbances) merged over the Southeastern USA. One came
from the southwestern U.S. and the other from over southwestern Canada. This
is described in a paper by Lance F. Bosart and six others at the State University
of New York at Albany. Bosart and his colleagues traced the Canadian disturbance
back to central North American almost a month earlier. They tracked the Southwest
disturbance back to multiple anomalies over the Atlantic and central Asia the
month before the storm. This is described in their paper, "Large-Scale Antecedent
Conditions Associated with the 12-24 March 1993 Cyclone ("Superstorm 93") Over
Eastern North America." It's in the preprint volume for the 14th Conference
on Weather Analysis and Forecasting, January 15-20, Dallas, Texas, published
by the American Meteorological Society in 1995. (11-4-96)

Q: What causes the tendency for winds to shift from
the south to the north (do I have this right?) when a cold front passes through?

A: You've got it right. A cold front is a boundary where
cold air mass is replacing a warmer air mass. The warm air is warm because the
winds are coming generally from the south. The cold air is cold because it is
coming from the north, where it's cold. As the boundary, the cold front, passes
an area, the wind will generally shift from the southwest to the northwest and
then eventually around to the north. In fact, the time the wind shifts is considered
the time of frontal passage at a weather station. A USA TODAY online graphic
on cold fronts shows what's going
on. The text with the graphic has links to other graphics that go into more
detail about air masses and what happens at fronts. (10-27-96)

Q: Which way would water drain if it were neither in
the Southern Hemisphere or the Northern Hemisphere but right in the middle of
the equator.

Q: If a tornado's winds circulate counterclockwise in
the Northern Hemisphere and clockwise in the Southern Hemisphere what would
happen to the winds if a tornado crossed the equator? Thank you

A: The first question, about water going down the drain,
is based on one of the most widespread myths in earth science. The myth is that
the Coriolis effect makes water drain differently
in the different hemispheres. But you can't blame people for believing this
myth because it's given as "fact" in some books and some teachers pass it along
to their students. The best explanation that I've found on why this is a myth
is the "Bad Coriolis"
section of the Bad Meteorology web site maintained by Professor Alistair
B. Fraser of Penn State University.

The rotation of tornado winds does not depend directly
on the Coriolis effect. This means that while most Northern Hemisphere tornadoes
have counterclockwise rotation, all of them don't. Scientists have taken videotapes
of a few clockwise tornadoes in the USA. But, big storms such as hurricanes
always have counterclockwise winds north of the equator, clockwise winds south
of the equator. Let's change the second question, making it: "What would happen
to a hurricane that crossed the equator?"

As you approach the equator the Coriolis effect becomes
weaker and weaker. If a hurricane started moving toward the equator, it would
begin falling apart because it needs the Coriolis effect to make the winds to
spiral into the center. This is why hurricanes don't occur near the equator,
much less cross it. (10-24-96)

Q: How do mountains form their own weather, and how
high must a mountain be to do so?

A: We have a mountain weather
index with links to graphics and text on some of the ways mountains influence
the weather. But, none of those directly address your question about how high
they have to be. Probably the best answer is "not very." In the Appalachians,
which aren't much in comparison to the Cascades near you in Seattle, even 3000-foot
high mountains tend to have more rain on snow on their tops than nearby lower
elevations. Of course, the higher the mountains, the more dramatic the weather
they help create. (10-1-96)

Q: What is the maximum wind speed ever recorded on land
or in a tornado, and when was it?

A: The highest wind gust ever recorded on land took place
on April 12, 1934, atop Mount Washington, N.H. This wicked gust, generated by
a huge spring storm, rattled a special
type of wind measuring instrument that determines a difference in air
pressure as the wind blows across two holes in it, rather than spinning
cups or fins fast or slow in relation to the wind speed. A calculation of the
pressure difference yielded a gust of 231 mph, the highest recorded anywhere
in the world to that date. This wind record still stands today and isn't likely
to be broken anytime soon. In 1965, an anemometer in Tecumseh, Mich., took a
direct hit by a tornado. Before
it was destroyed, it recorded a 151-mph wind gust at 33 feet above the ground
- official anemometer height. Most wind instruments are destroyed by flying
debris well before a tornado's winds reach their peak, but this one was momentarily
lucky. A portable doppler radar, toted into
the field to study tornadoes by Professor Howard Bluestein, Ph.D., of the University
of Oklahoma, used microwaves to "measure" wind velocity at an incredible 288
mph, verifying, for the first time, a tornado's winds in the F5 range of the
Fujita tornado intensity scale. The twister
that spun up this terrible wind was the infamous Red Rock, Okla., tornado of
April 26, 1991; this date might sound familiar since it was the same day another
F5 tornado obliterated the Golden Spur Mobile Home Park in Andover, Kan.

Answered by Chris Cappella, USA TODAY Information Network.
(9-8-96)

Q: What is an occluded front?

A: It's a complex boundary between warm, cool and cold
air masses.Cold
and warm fronts are boundaries
only between cold and warm air. A USA TODAY online graphic explains more about
occluded fronts. (8-27-96)

Q: Is it me or do most of our weather systems seem to
run in a seven day cycle? It seems like every time a storm hits on the weekend,
the next weekend is stormy also. What do you think?

A: At times weather does seem to run in the kinds of cycles
you've noticed, but they don't last. In the 1930s meteorologists spent a lot
of time trying to use cycles for predictions. But the method didn't turn out
to be reliable. So many factors go into determining the weather that it doesn't
fall into regular cycles for long. Our forecasting
home page has more information on this. (7-31-96)

Q: In the Chicago area July 18, 1996 we had a mesoscale
convective complex that produced record rainfall (17 inches in Aurora and Naperville).
I was told that such MCC's only occur at night. Can you tell me more about this
weather condition? I heard that the condition occurred again in our area last
night, July 30, 1996.

A USA TODAY online graphic
explains these complexes of thunderstorms that form at night, but can last
into the next morning. Another graphic explains how
they form. MCC's supply much of the summer rain in the central USA. MCCs
also brought most of the rain that caused the major flooding in the upper Midwest
during the summer of 1993. (7-30-96)

Q: How can a storm coming from the west rip my roof
shingles off, as if it were coming from the east?

A: Storms consist of winds swirling around a low pressure
center - counterclockwise in the Northern Hemisphere. Think of the storm as
being like a merry go round that's turning counterclockwise as a flat-bed truck
carries it east, at a slow speed, say maybe 15 mph. If people on the merry go
round were holding out their hands, they would hit things along the north side
of the road from the east side. This would be like the winds of the storm hitting
things from the east even though the entire storm is moving toward the east.
By the way, Benjamin Franklin is credited with being the first person to figure
this out about storms. A USA TODAY online
graphic has more on storms.(4-30-96)

Q: What is the jet stream? How does it form? How is
it different from a front? Does one affect the other?

A: The jet
stream is a high-altitude river of fast-moving air with wind speeds of 57
mph or greater. The two main jet streams that influence the USA's weather are
the polar jet and the subtropical jet stream. A front is a boundary between
different air masses. Warm, cold,
stationary, and occluded
fronts all have different implications for the weather. The jet stream and the
polar front are very closely linked together. The polar front refers to the
main cold front that separates cold, polar to the north from warm, tropical
air to the south. Air movements associated with the polar front lead to the
development of the jet stream. An USA TODAY Online graphic explains more about
the formation of jet streams.

(Answered by Chad Palmer of USA TODAY Information Network)
(3-27-96)

Q: Much has been written about the "El Nino" effect
on the weather. Here in Australia, it would seem that our weather patterns are
influenced even more profoundly by this effect than in other areas of the world.
Could you please explain this effect in layman's terms?

Q: You're correct, the complex weather pattern known as
El Nino can have major influences on Australia's weather. For example, it's
often linked to droughts there. You can begin learning about it by going to
our El Nino page where you you'll find
links to explanations starting on a beginner's level. You'll also find links
to various government and other sites with more detailed information and updates
on what's going on. (3-22-96)

Q: We're from the Hong Kong International School and
are doing a weather unit. We would like to ask you a few questions:

How is a low pressure system different from a high
pressure system?

What are some factors that determine the speed of
wind?

What is an occluded front?

A: You're in luck, USA TODAY Online has produced graphics
on each of your questions. Just click on the words highlighted in color to go
to these graphics. One of our online graphics compares high
and low pressure areas. It should answer your question. We have two other
graphics that should help, one takes a closer look at low
pressure, the other at high pressure.
The wind's speed is determined primarily by what's known as the pressure
gradient force, or the difference in air pressure and the distance over
which this difference operates. High pressure "pushes" wind toward low pressure.
An occluded front is a complex
area of boundaries between cool air, cold air and warm air
masses meet. You might also want to look at our graphics on cold
fronts, warm fronts, and stationary
fronts. Finally, fronts are usually part of large weather systems known
as extratropical storms. If the
graphics I've noted here don't answer all of your questions, you can check our
How the Weather Works index for more. We
also have a detailed index to all of our graphics.
If you still can't find an answer, send in another Ask Jack question. We've
done many of our graphics in response to questions.(3-20-96)

Q: I've always been curious about wind, but have never
been able to find any statistics relating to it, such as the windiest spot in
the USA. Are any such statistics available?

A: The National Climatic Data Center (NCDC) in Asheville,
N.C., which keeps all of the nation's weather records, compiled a list of the
"windiest cities" a few years back, which I used in my USA
TODAY Weather Almanac. According to this list, Blue Hill, Mass., which is
near Boston, is the windiest place with an annual average wind speed of 15.4
mph. The second and third windiest places on this list are Dodge City, Kan.
with 14.0 mph and Amarillo, Texas with 13.5. Rochester, Minn., is fourth with
13.1 mph. Of the six others in the top 10, all are on the western Plains except
Boston, which comes in ninth with 12.5 mph.

But, a glance at the NCDC booklet "Comparative Climatic
Data for the United States Through 1991" shows that St. Paul Island, Alaska,
has an annual average wind speed of 17.6 mph and Cold Bay Alaska has 17.0 mph.
Both Barter Island, Alaska, and Bethel, Alaska, would make the top 10. In many
cases, figures from Alaska and Hawaii aren't used in official U.S. climate lists.
Also, the lists are from regular weather stations and don't include places such
as the weather station atop Mount Washington, N.H., which has an annual average
wind speed of 35.3 mph, according to the NCDC booklet. (3-19-96)

Q: On television I hear the weather term "short wave"
used. Could you give me a brief definition of this term. Thanks

A: Let's start with long waves. When you see charts of
the upper air winds or the jet stream, you'll notice that sometimes they make
a wavy pattern with the jet stream coming down over the South and then back
over the North. A USA TODAY Online graphic shows
this and what it means. Anyway, one of these "long waves" in the flow of upper-air
winds can stretch across the U.S. "Short waves" are "kinks" in these long-wave
patterns. While the long waves can stay in place for days, the short waves travel
along with the winds. Such short waves can bring clouds and rain. They are also
called "upper-air disturbances." We have another
online graphic with more on what they do. (3-13-96)

Q: We were wondering if you could give us some useful
information how air masses form. We are sixth graders at Centennial Middle School.
Thank you for your help.

A: You've probably learned already that air masses are
huge areas of air with roughly the same temperature and humidity near the ground.
By huge, I mean the air covering several U.S. states. They can be cold and dry,
cold and humid, warm and dry or warm and humid. Air masses form when air stays
for days over land or water that's either warm or cold. They take on the characteristics
of the surface they're over. Cold air masses form over cold places, warm air
masses over warm places. Those that form over land are dry, those that form
over water become humid. Eventually, the air masses begin moving to bring cold
or warm, dry or humid weather. Your question prompted us to prepare a USA TODAY
Online graphic showing where the different air masses that affect the USA's
weather come from. Text with the graphic tells more about each kind of air mass.
Click here to go to the graphic
and text. (3-12-96)

Q: What is the Coriolis effect? (In plain English please)

Q: Can you explain the Coriolis effect, and how it differs
in the northern and southern hemisphere's? Is it in fact an effect ora
force?

A: Coriolis effect, or force, refers to the turning of
wind, ocean currents, rockets, and other things moving across the Earth's surface.
In simple terms, you can think of Coriolis being caused by the Earth's rotating
under the object, which moves in a straight line in relation to space. Objects
turn to the right of their direction of motion in the Northern Hemisphere, to
the left south of the Equator. Coriolis is zero at the equator, greatest at
the poles. When you are working out the mathematics of Coriolis you treat it
as though it is a physical force. But, since it's not really a force it's probably
better to call it the Coriolis effect. A USA TODAY Online
graphic and text has more information, including who it's named after. (3-10-96)

Q: What is an Alberta Clipper?

A: The term refers to extratropical
cyclones that form just east of the Rockies in Alberta, Canada. The storms
then usually move quickly eastward - like a fast clipper ship - to the Great
Lakes region and then on to the East Coast. Typically they bring light snow
because they're moving so quickly. Sometimes the winds around the storm's center
push frigid air southward into the Midwest and East. From time to time a clipper
will strengthen into a fierce northeaster
off the Atlantic Coast. A USA TODAY Online
graphic has more information on Alberta Clippers. (2-29-96)

Comment: Could you explain a storm referred to as a
"nor'easter"? Is it a scientific weather term, or an old time expression that
refers to local storm activity that approaches from the northeast?

Q: When reference is made to a winter storm as being
a "northeaster" does this refer to the storm tracking towards the northeast
or tracking from the northeast. Also, when a wind is described as easterly does
this refer to the wind going from the east or going towards the east. I seem
to find both uses or am I misinterpreting?

A: Good time to ask this question. The Jan. 7-8 blizzard
was a "northeaster" and the storm expected to hit the East on Friday, Jan. 12,
will be another. Forecasters use the term, but it really is an old-time expression
that refers to the fact that as a storm's low-pressure center moves northward
off the East Coast, the counterclockwise winds around it will first blow from
the Northeast as the storm moves by. This is the first shot of rain, snow or
ice. Since the swirls of winds around such storms are several hundred miles
across they can blow from the northeast for a long time if the storm is moving
slowly. As the storm's center moves on north of a particular location, the winds
will shift around to blow from the Northwest, normally bringing colder but drier
air. A USA TODAY Online graphic
has more information.

On wind direction, I'm sure you do hear the term "easterly"
used to refer to winds both toward and front the east. But, in meteorology,
wind direction refers to the direction the wind is coming from. Thus, an "easterly"
wind is blowing from east to west. (1-11-96)

Q: Love the USA TODAY Online weather information. I've
seen weather maps showing weather fronts. The lines usually have rounded "nodules"
or sharp triangles along them. What do these mean? Why are they sometimes colored
either red or blue? Why are they sometimes on one side of the line or the other?
Thanks!

A: If you click on the highlighted names of the fronts
in the following answer, you'll go to USA TODAY Online graphics explaining more
about what fronts are and what's going on along them. A blue line with the triangles
donates a cold front with the
triangles pointing the direction the front is moving. A red line with the rounded
"modules" is a warm front with
the circles on the side toward which the front is moving. A red and blue line
with both triangles and circles, pointing in different directions represents
a stationary front. .

You might also want to check out the Weather
Map Legend on the Purdue University Web site. It shows all of the common
symbols. And for more about what it all means, go to our weather
forecasting page.

Q: Hi Jack! I have a meteorological quandary. I am a
little confused about the Coriolis effect in the Northern Hemisphere. Is there
any relationship between the migrating Northern magnetic pole and counter-clockwise,
cyclonic rotation around low pressure areas? Thanks for the help! I love your
service.

A: There's no connection between the Coriolis effect and
magnetism, which means there is no connection between the slow migration of
the magnetic poles and air movements. By the way, "cyclonic rotation" refers
to wind movements around low-pressure areas, which is counterclockwise in the
Northern Hemisphere and clockwise south of the equator.

A USA TODAY Online graphic illustrates the Coriolis
effect. It shows that Coriolis is the result of the Earth's rotation. Another
graphic shows how pressure forces push the
winds. We haven't yet done a graphic showing how the pressure and Coriolis forces
make wind move counterclockwise around low pressure in the Northern Hemisphere
and clockwise in the Southern Hemisphere. Let me draw a word picture.

Imagine a "parcel" of air, that is a "chunk" of air of
any size, between a high-pressure and a low-pressure area in the Northern Hemisphere.
The pressure force pushes the air from the high toward the low pressure area.
Once the air parcel begins moving, the Coriolis effect makes it begin turning
to its right. Eventually, the air parcel is heading at right angles to its original
path. Coriolis is still trying to push it to the right, but now the pressure
force is pushing it back to the left. The balance between pressure gradient
and Coriolis forces will keep the air parcel going to the left around a low-pressure
area.

Near the Earth's surface, friction slows the air, which
reduces the Coriolis effect. The result is that the pressure gradient force
will be stronger and the air will spiral in toward the center of the low
pressure area, where it rises. Graphics in my USA
TODAY Weather Book illustrate all of this.

Q: Why do cold fronts move faster than warm fronts?

A: The main reason cold
fronts usually move faster than warm
fronts is that the cold air behind the cold front is heavier and more dense
than the warm air behind the warm front. The heavier, denser, cold air can push
the warmer lighter air ahead of the cold front out of the way much easier than
the warm air can push the cold air ahead of the warm front.

In fact, warm air never really "pushes" the cold air out
of the way. Instead the warm front's movement depends on how fast the cold air
is retreating. When warm, lighter air clashes with cold, heavier air, the warm
air almost always rises up and over the cold air at the surface.

For example, suppose you have a Mack truck and a small
compact car. The Mack truck, representing the cold air, can push the small compact
car, representing the warm air, along with ease. However, the small compact
car would have a lot of difficulty trying to push the Mack truck along.